Block copolymers in which two or more chemically distinct polymer chains are linked by covalent bonds can be separated into regular microphases due to their self assembly characteristics. The microphase separation phenomenon of such a block copolymer is generally explained by volume fractions, molecular weights and mutual attraction coefficients (Flory-Huggins interaction parameter) between constituents, and it may form various structures with nano-scale spheres, cylinders, gyroids or lamellae, and the like.
An important issue in practical applications of various nanostructures formed by the block copolymers is to control orientation of microphases of the block copolymer. If the spherical block copolymer nanostructure is a zero-dimensional structure having no direction of special orientation, the cylindrical or lamellar nanostructure has orientation as one-dimensional and two-dimensional structures, respectively. Typical orientation properties of the block copolymer may include a parallel orientation in which the orientation of the nanostructure is parallel to the substrate direction and a vertical orientation in which the orientation of the nanostructure is vertical to the substrate direction, where the vertical orientation often has greater importance than the parallel orientation.
Typically, the orientation of the nanostructure in the film of the block copolymer can be determined by whether any one of the blocks of the block copolymer is exposed to the surface or air. That is, the orientation of the nanostructure can be determined by selective wetting of the relevant block, where since a plurality of substrates is generally polar and air is non-polar, a block having a larger polarity in a block copolymer is wetted on a substrate and a block with a smaller polarity is wetted at the interface with air, whereby the parallel orientation is induced.